1. Field of the Invention
Embodiments of the present general inventive concept relate to an image forming apparatus to detect the toner density of a developer and a control method thereof.
2. Description of the Related Art
Generally, an electrophotographic printer prints a black and white image or a color image by scanning light onto a photosensitive medium charged to a predetermined potential, thereby forming an electrostatic latent image, developing the electrostatic latent image with toners of predetermined colors in a developing device, and transferring and fixing the developed image onto a sheet of paper.
Electrophotographic printers are categorized into wet-type electrophotographic printers and dry-type electrophotographic printers according to the types of developers used in them. A wet-type electrophotographic printer uses a developer containing a powder toner scattered in a liquid carrier, whereas a dry-type electrophotographic printer uses a two-component developer containing a powder carrier and a toner, or a single-component developer containing a toner only.
In order to print a full-color image, color toners of yellow (Y), magenta (M), cyan (C), and black (K) are required. Thus, four developing devices are also required, each for developing one of the four color toners. A full-color image can be formed by a single path method using four exposurers and four photosensitive media or by a multi-path method using a single exposurer and a single photosensitive medium.
To get a uniform and good-quality color image, many bias parameters such as a charge voltage, a development voltage, a transfer voltage, etc. should be determined and applied. Density gradation and stability are particularly critical factors to determine image quality in an image forming apparatus that forms overlapped images on a photosensitive medium or an intermediate transfer belt and transfers the overlapped images onto a sheet of paper at a time.
Accordingly, to maintain an accurate density of a color image, a color image forming apparatus using a photosensitive medium or an intermediate transfer belt forms a density measurement patch of a predetermined type on the photosensitive medium or the intermediate transfer belt and determines a plurality of bias parameters by measuring the toner density of this patch using a density sensor.